Cam with balanced spring-loaded followers



VELOCITY HNJ SEC.)

Dec. 1, 1970 E. F. LOUGHRAN, JR 3,543,589

CAM WITH BALANCED SPRING-LOADED FOLLOWERS Filed Dec. 20, 1967 2Sheets-Sheet l FIG! vI i i E x INVENTOR EUGENE FRANCIS LOUGHRAN BY//M%%% ATTORNEY TIME Dec. 1, 1970 E. F. LOUGHRAN, JR

CAM WITH BALANCED SPRING-LOADED FOLLOWERS 2 Sheets-Sheet 2 Filed Dec.20, 1967 INVENTOR. 5066M: F lous/maqqdq ljmw PM T P P ajwmfiiwm smmmm. mH.

United States Patent 3,543,589 CAM WITH BALANCED SPRING-LOADED FOLLOWERSEugene F. Loughran, Jr., Oakville, Conn., assignor to North AmericanPhilips Corporation, New York, N.Y., a corporation of DelawareContinuation-in-part of application Ser. No. 466,963, June 25, 1965.This application Dec. 20, 1967, Ser.

Int. Cl. F16h 25/16 U.S. Cl. 7454 11 Claims ABSTRACT OF THE DISCLOSUREThis is a continuation-in-part of my co-pending application Ser. No.466,963 filed June 25, 1965.

This invention relates to a cam with balanced springloaded followers andparticularly to a cam usable in a cam-actuated switch assembly for arepeating interval timer or the like as shown and described in KavanaughPat. 2,953,667 and Haydon Pat. 3,106,620.

-In cam-actuated switches of the type described in the Kavanaugh andHaydon patents, supra, a small electric motor is required to supplysuflicient power to drive a plurality of cams each of which actuates anumber of switch contacts mounted on spring blades. Some of the switchblades are arranged so they bear against only one side of the cam whileothers are arranged in balanced pairs so that they provide substantiallyequal and opposite forces to offset each other so as not to create anyside loading on the bearings for the cam. However, in all of theforegoing cam-actuated switches, each cam has either had its camfollowers acting onlyon one side of it or, if it had balanced camfollowers, the cam had an even number of equal lobes. Thus, in eithercase the motor had to supply sufficient power to rotate the cam and toaccelerate the followers. The loading of the cam followers, where thereare two of them operating on identical lobes and both moving in togetherand out together, is additive. The torque available from the motor couldbe effectively increased by gearing down the speed of the motor butwhere there is a minimum speed of operation of the cam and a maximumspeed of operation of the motor, or perhaps a fixed synchronous speed ofthe motor, there is a limit to the number of gears that can be used.There is also some loss, although it may be very small, in eachadditional gear.

When a spring blade forces a cam follower against the surface of a cam,several forces are produced that must be overcome by the torque of themotor that drives the cam. For one thing the follower may exert a directfrictional drag on the cam. This can be reduced within limits by usingroller followers having low inherent friction, or by suitablelubrication, or both. Even so, there is still some drag, and this isrelated to the force of the spring that presses the follower against thesurface of the cam. In addition to supplying the pressure that producesthe friction loading of the cam follower on the cam, the spring producesa force of its own that must be overcome by the torque of the motor, aswill be discussed hereinafter. Another force arises from the product ofthe mass of the follower times the acceleration that the follower3,543,589 Patented Dec. 1, 1970 ice has to undergo. Thus if the cam hasa rather steep incline that forces the follower against the pressure ofits spring, there is a force which is proportional to the secondderivative with respect to time of the movement of the cam followeralong the inclined surface. This force is also proportional to the massof the cam follower and can be reduced by reducing the mass, but again,in any design there is always a minimum mass for that particular designand once this has been reached, the only way of reducing this force isto reduce the acceleration of the follower, which is the same thing asreducing the rate of change of velocity of the follower with respect totime.

The present invention proposes an additional cam follower as a novelmeans of overcoming or, more properly, compensating part of the forcesexerted on the motor that drives the cam. In accordance with the presentinvention a cam having an odd number of lobes is used with at least twocam followers acting on diametrically opposite points of thecircumference. In this way, as one of the followers is being pushedoutwardly away from the axis of the cam, energy is stored in it.Simultaneously the other follower is moving inwardly toward the axis ofthe cam and is returning its previously stored energy to the cam, thusproviding an additional force that tends to assist the cam in rotating.This is opposite to the force that is required to thrust the other camfollower outwardly and thus tends to reduce the total amount of torquerequired of the electric drive motor. By proper formation of the lobes,the energy withdrawn from the cam by one follower can be nearly matchedat any time by the energy returned to the cam from the other follower.

Further in accordance with the invention, the cam lobes are shaped so asto reduce the initial velocity of the cam followers. Since accelerationis proportional to the rate of change of velocity with respect to time,reduction in initial velocity also reduces the rate that the velocitychanges initially and this means that the initial acceleration, whichrequires much of the torque of the motor, is reduced.

The invention will be described in greater detail hereinafter inconnection with the drawings in which:

FIG. 1 shows a side view of a cam-actuated switch constructed accordingto the invention with part of the outer shell broken away to disclosethe operating mechanism;

FIG. 2 is a cross-sectional view along the line 22 in FIG. 1 of a camand follower mechanism in the switch of FIG. 1 constructed according tothe invention;

FIG. 3 shows the apparatus of FIG. 2 at a different point in theoperating cycle of the cam;

FIG. 4 is a graph of velocity versus time of the contacts in theswitches of FIGS. 2 and 3;

FIG. 5 shows a different embodiment of the invention comprising a camhaving an even number of lobes;

FIG. 6 shows an embodiment of the invention in which the cam followersare not diametrically opposite each other;

FIG. 7 shows an embodiment of the invention comprising an internal cam;and

FIG. 8 shows an embodiment of the invention comprising a disc cam.

The cam-actuated switch in FIG. 1 has an outer housing 11 and aplurality of contact pins 12 at one end to fit into a standard socket.The operating mechanism includes a motor 13, which may be governed orsynchronous, constant speed motor mounted on a plate 14 and providedwith a pinion 16 that meshes with a larger gear 17 rotatably mounted onan axle 18. The gear is rigidly connected to a first cam 19 and to asecond cam 21 constructed according to the present invention. Inaddition the gear 17 is connected to a shaft 22 and through the latterto additional elements that play no part in the present invention andtherefore are not shown. The plate 14 is attached by means of spacerrods, one of which is indicated by reference number 23, to other partsof the cam-actuated switch that must be supported rigidly with respectto the motor 13.

Several cam followers 25-28 are shown, each supported on its ownresilient arm 30-33, respectviely. The specific form of the camfollowers and the means of mounting the followers is described andclaimed in Kavanaugh Pat. 2,953,667, supra, and reference may be had tothat patent for further description. In addition the relative spacingsand arrangements of the cam followers 25-27 and their arms 30-32 may beconstructed in accordance with the Haydon Pat. 3,106,620. 1

The arm 33 is provided with a contact that is attached to a spur 34extending from one side of the arm. This contact may be welded in placeor afiixed by any other convenient means and is not visible in FIG. 1although the Weld mark 36 is shown there. This contact cooperates with afacing contact 37 on a resilient arm 38 located close to the arm 33-.

In the design of switches of the type illustrated by the cam follower28, its arm 33, the spur 34, and the contact 37 with its arm 38, theengineering specifications may include not only the spacing between thecontacts when they are separated by a maximum amount but also thedistance through which the cam follower 28 must move beforedisengagement of the two contacts is effected, as well as the pressureof both of the resilient contact arms 33 and 38 and even the velocity ofthe cam follower at the instant of separation of the two contacts fromeach other or at the instant of their coming together again. All ofthese requirements make the design of a satisfactory cam-actuated switchfar from the simple matter it would appear to be on its surface.

FIG. 2 shows the cam 21 and the follower 28 in greater detail. As may beseen, the cam 21 has five lobes 21a21e. The cam follower 28 is in theform of a roller having a stub axle 39 snapped into a recess formed inthe end of a bent-over tab 41 at the end of the arm 33 and having anentrance smaller than the diameter of the axle 39. There are actuallytwo such tabs, but the other is directly behind the tab 41 and thereforedoes not appear in this drawing.

The contact mounted on the spur 34 is indicated by reference number 42and is directly facing another contact 37 supported by the arm 38. Thisarm is partly positioned by a more rigid arm 43 that determines thelimit of motion of the contact 37 to the left, as the contact is shownin FIG. 2. The arm 38 is formed with a certain resilient force againstthe arm 43, although this resilient force may be less than the forceapplied by means of the contact 42 when follower the 2 8 is farthest tothe right. In the position shown in FIG. 2 there is no force of thecontact 42 upon the contact 37 because the arm 33 is as far left as itwill go in normal operation. Matching the cam follower 28 but on theother side of the cam 21 is a second follower 44 of similar dimensions.This follower has its own stub axle 46 held within a recess in the endof a bent-over tab 47 formed at the end of a resilent arm 48. The lattercorresponds exactly to the arm 33 and has a contact 49 in juxtapositionto another contact 51 on the end of a resilient arm 52 that matches thearm 38. A relatively rigid arm 53 limits the movement of the contact 51to the right.

FIG. 2 shows the cam 21 in a position such that the cam follower 28 ison the peak of the lobe 21e while the cam follower 44 is in the bottomof the pocket formed between the lobes 21b and 210. The contact 49 is asfirmly pressed against the contact 51 as the resilient forces in thearms 48 and 52 will permit while the contact 37 is as much separatedfrom the contact 42 as the construction will allow. Any rotationwhatsoever of the cam 21 from the position shown will cause the follower28 to slide 4 down from its peak and will correspondingly cause thefollower 44 to move outwardly. Assuming that the rotation is clockwisethe cam follower 28 will slide down that face of the lobe 21e toward thepocket between the lobes 21a and 21e while the follower 44 will start torise up the slope of the lobe 210.

In the absence of any other forces, the pressure of the arm 33 on thefollower 28 and from the follower 28 onto the downward slope of the lobe21e would cause the cam 21 to rotate until the follower 28 came to restin the pocket between lobes 21a and 21s, as shown in FIG. 3. In doing sothe spring arm 33 would give up the energy stored in it in moving fromthe pocket between the lobes 21d and 21s to the peak of lobe of 21e.Moreover, by proper design of the contour of the lobes of the cam 21,the amount of energy given up by the arm 33 to the cam at any instantwould be substantially equal to the amount of energy withdrawn from thecam 21 by the arm 48 at the same instant.

0f course it is impossible to compensate the withdrawn energy by thereturned energy precisely; there is always a small amount of energy thatis lost and the shapes of the cam lobes are such that slightly moreenergy may be withdrawn at any given instant than is being replaced orvice versa. Even so, and taking into account that there will be a netloss overall, there is still a net gain with respect to the conditionthat would prevail in the absence of one of the cam follower systems.That is, if the cam follower 44 and the arm 48 to which it is attachedwere removed from any contact with the cam 21 so that only the camfollower 2-8 rode upon the surface of the cam 21, the torque required ofthe motor would be significantly greater than it is when there are twospring-loaded cam followers 28 and 44.

FIG. 4 is a graph of the velocity of one of the cam followers, forexample, the follower 28 with respect to time. It is desired that thecontacts 42 and 37 separate at a predetermined time T In addition thevelocity of the contact 42 at the instant of separation should berelatively high so that there will be a clean break in the electricalcircuit. Heretofore this has meant that the cam lobes would have to beshaped so as to start the motion of the cam follower suddenly asindicated by the dotted vertical line 54 at the left-hand part of thegraph. Following the studden start, the velocity of the cam followerwould decrease along the dotted curve 56 to the desired velocity at thetime T As stated hereinabove, the ac celeration is the rate of change ofvelocity with respect to time and the force required to set the camfollower suddenly into motion is proportional to this acceleration. Asmay be seen by inspection of the line 54, its slope is quite steep andin fact is almost vertical, which means that the acceleration is veryhigh and therefore the force required to produce this acceleration iscorrespondingly high. Since this force must be produced by the motor astorque, the minimum torque of the motor must be at least high enough toproduce the initial acceleration of the follower, plus, of course, otherloads in the rest of the device. However, the torque required toaccelerate the followers is a significant part of the total torquerequired of the motor.

In accordance with the present invention, the lobes 21a-21e of the cam21 have been shaped so that the velocity of each of the cam followers'28 and 44 changes rather slowly from zero to a maximum which is notmuch greater than the value at the time T This relatively slowlyincreasing velocity is indicated by the curve 57. The maximum slope ofthis curve is very much less than the line 54 and therefore theacceleration is also very much less. Thus, the force required to moveeven one of the cam followers 28 or 44 by means of the cam lobe shapedas shown in FIGS. 2 and 3 is minimized. In addition the lobes are soshaped that the acceleration of the cam follower 28, for example, towardthe center of the shaft 18 to the peak of the lobe 28a, for example,

is approximately the same as the acceleration of the cam follower 44radially away from the axis of the shaft '18 along surface of the camlobe 210, for example. This permits the energy stored in the resilientarm 33 to be given back to the cam in about the same measure as energyis withdrawn from the cam.

In order to balance out radial forces on the cam, the cam followersshould strike diametrically opposite points of the cam surface. Thisrequires that the cam have an odd number of lobes so that one of thefollowers can be on the peak of one lobe while the diametricallyopposite follower is in the center of a pocket between two lobes. If aradial force can be tolerated, as it frequently can, the cam may have aneven number of lobes and one of the followers may be displaced so thatit is not diametrically opposite the other follower. Such a structure isshown in FIG. 5 in which the cam 121 has six lobes 121a121f. Thefollowers are the same as in the embodiment in FIGS. 2 and 3 and havebeen given the same reference numerals, and except .for the fact thatthe follower rollers 28 and 44 are not exactly diametrically opposed,the operation of this embodiment is the same as that in FIGS. 2 and 3.The follower rollers 28 and 44 are angularly disposed around the cam 121so that they are 180 operating degrees out of phase with each other,that is, as the roller 28 is rolling up the inclined leading surface ofone of the lobes, for example, lobe 121d, the roller 44 is rolling downthe falling surface of one of the other lobes, in this case the lobe121a. This permits the cam follower roller 44 to give energy that hasbeen stored in the spring 48 back to the rotating cam mechanismsimultaneously with and in approximately the same amount as the amountof energy being withdrawn from the cam operating mechanism by the roller28 and being stored in the spring 33.

Another structure in which there is an even higher unbalanced radialload on the cam is shown in FIG. 6, which has the same five-lobed cam 21as in FIGS. 2 and 3. However, the follower roller 44 and componentsconnected to it have been moved so that it is no longer diametricallyopposite the cam follower 28. Instead of being on top of the lobe 210when the follower roller 28 is centered in the pocket between the lobes21a and 21a, the follower roller 44 is shown at the instant that itrests on the peak of the lobe 21b. Again, the follower roller 44 is 180operating degrees out of phase with respect to the follower roller 28.

It is not necessary that the rollers operate on external carn surfaces.FIG. 7 shows a similar operation utilizing an internal cam 221. Thestructure in FIG. 7 uses relatively small diameter follower rollers 128and 144 which have relatively much smaller radii than the radius ofcurvature of the pockets between the inwardly-directed lobes 221a-221ein contrast to the rollers 28 and 44 in FIG. 2, which have radii onlyslightly smaller than the radius of curvature of the pockets between thelobes 21a21e. The follower rollers 128 and 144 are shown diametricallyopposed to each other and they are also 180 operating degrees out ofphase.

The followers in the embodiments described hereinabove have all operatedon cylindrical cam surfaces. However, the energy-balancing effect of theinvention can also be realised in the case of a disk such as the cam 321shown in FIG. 8. In this case, the cam has a multiplicity of lobes ofwhich only the lobes 321a and 321 are shown. These lobes form an axiallyfluted surface on the cam 321. As may be seen, one of the followerrollers 228 is centered in the pocket between the lobes 321a and 321b,at the same time that the other follower roller 244 rests on the top ofthe lobe .321f. Except for the fact that the follower rollers pressaxially against the cam surface of the cam 321, the operation is thesame as in the earlier embodiments and energy stored in the resilientmember 133 will be returned to the cam 321 6 at the same time that theresilient member 148 is extracting energy from the cam.

While this invention has been described in terms of a specificembodiment, it will be understood that modifications can be made thereinwithout departing from the true scope of the invention.

What is claimed is:

1. Cam and follower mechanism comprising: a cam rotatably mounted on anaxis and having a cam surface divided into a plurality of substantiallyidentical, symmetrical, continuously rounded lobes separated from eachother by the same number of pockets, each of said pockets having apredetermined contour; and a pair of followers disposed about the camand separated by substantially operating degrees, each of said followershaving substantially identical convex portions bearing upon said camsurface, and separate and substantially equal resilient means supportingeach of said followers and forcing said followers into contactsimultaneously with said cam surface at all times whereby energy storedin one of said resilent means when the cam follower supported there-byis on a rising portion of one of said lobes produces a torque on the camthat is substantially equal and opposite to the torque resulting fromthe transmission of energy from the other of said resilient meansthrough the cam follower supported thereby to the following portion ofthe lobe against which said last-named cam follower is pressed.

2. The cam and follower mechanism of claim 1 in which said cam surfaceis a cylindrical surface.

3. The cam and follower mechanism of claim 2 in which said convexportions of said followers are on diametrically opposite sides of saidcam surface and in which the number of said lobes is odd and at least asgreat as five.

4. The cam and follower mechanism of claim 2 in which said cam surfaceis an external cylindrical surface of said cam.

5. The cam and follower mechanism of claim 2 in which said cam surfaceis an internal cylindrical surface of said cam.

6. The cam and follower mechanism of claim 1 in which there is an evennumber of said lobes.

7. The cam and follower mechanism of claim 1 in which said cam is an endcam and said cam faces in an axial direction.

8. The cam and follower mechanism of claim 1 in which each of saidpockets has a predetermined minimum radius of curvature and each of saidconvex portions has a radius of curvature slightly less than the minimumradius of curvature of said pockets.

9. The cam and follower mechanism of claim 1 in which each of saidpockets has the same predetermined minimum radius of curvature and eachof said convex portions has a radius of curvature substantially lessthan the minimum radius of curvature of each of said pockets.

10. Cam and follower mechanism comprising: a radial disk cam rotatablymounted on its axis and having a cam surface divided into an odd numberof substantially identical, symmetrical, continuously rounded, convexlobes separated from each other around the periphery of said cam by thesame number of concave pockets, each of said pockets having apredetermined contour; and a pair of diametrically opposed convexfollowers bearing upon said cam, each of said followers having a contoursubstantially equal to said contour of said pockets; and separatesubstantially equal resilient means supporting each of said followersand forcing said followers into contact simultaneously withdiametrically opposed portions of said cam surface at all times wherebythe force of acceleration of one of said followers being urged radiallyoutwardly by the inclined portion of one of said cam lobes issubstantially equal and opposite to the force of acceleration of theother of said cam followers being urged radially inwardly by itsresilient means against the diametrically opposed portion of the camsurface to minimize the net force opposed to the rotation of said camdue to acceleration forces of said followers.

11. The cam and follower mechanism of claim 10 in which said followersare rollers rotatably supported on said resilient means.

References Cited UNITED STATES PATENTS 671,330 4/1901 Clemens 74541,317,365 9/1919 Greenberg 7454 2,107,373 2/ 193 8 Edwards 74572U.X.2,185,882 1/ 1940 Bedford 7454 2,489,626 11/ 1949 Doucette 74527U.X.

' 8 2,399,906 5/1946 Bentley 74527 2,953,667 9/ 1960 Kavanaugh.

3,106,620 10/1963 Haydon.

OTHER REFERENCES Rothbart, H.A.: Cams Design, Dynamics and Accuracy, NewYork, John Wiley and Sons, Inc., 1956, chapter I, pp. 12 and 13.

FRED C. MATTERN, JR., Primary Examiner F. D. SHOEMAKER, AssistantExaminer US. Cl. X.R.

